Extruder screw with long wearing surfaces

ABSTRACT

A method of extending the life of an extruder screw by affixing tiles of wear-resistant material along the crest of the extruder screw flighting threads, and optionally grinding the hardened material to remove any sharp edges. In another configuration of the present invention, plates of wear-resistant material are secured to the leading edges of the extruder screw threads to further prolong the life of the extruder screw.

CLAIM OF PRIORITY

This application claims priority from U.S. Provisional PatentApplication No. 60/569,633 entitled “EXTRUDER SCREW WITH LONG WEARINGSURFACES” filed on behalf of Edward Williams, on May 8, 2004 (AttorneyDocket No. GOEA 02869 PTPV), which is incorporated herein by referencefor all purposes.

CROSS-REFERENCE TO RELATED APPLICATION

This application also related to co-pending U.S. Patent Application No.______, entitled “DIE FOR EXTRUDED MATERIALS”, filed herewith on behalfof Edward Williams (Attorney Docket No. GOEA 02868 PTUS), which isincorporated by references for all purposes.

TECHNICAL FIELD

The invention relates generally to extrusion equipment, moreparticularly to extrusion screws, and most particularly to extrusionscrews that have been modified for extended wear and durability.

BACKGROUND

Extrusion is a well-known process that is used in many industries. Avariety of products from foods to optical fibers, plastics and metalsare produced by extrusion. In the extrusion process, the materials to beextruded are fed into the extruder, a type of giant mixer. The materialsare mixed, heated if appropriate, and fed into a barrel that contains aninternal rotating screw. The screw moves the liquid or viscous materialbeing extruded (the “extrudate”), out the end of the extruder, through adie having the shape of the desired product. The extrudate will take theshape into which it is formed coming out through the extruder die. Theextrudate is generally continuous, and is often cut into desired lengthsafter being extruded out the die. Extrudate is formed into an almostinfinite variety of shapes, ranging from tubes to sheet material.

It has been found that the outside edges of the screw threads in theextruder, which mix the extrudate and push it out the end of theextrusion barrel, tend to be more subject to wear than other parts ofthe screw threads. When the outside edges of the screw threads wearsufficiently, extrudate flows between the screw threads and the barrel,which interferes with the normal extrusion process. To this end, stepshave been taken to extend the durability on those parts of the screwsthat see additional wear. Such steps have included applying a coating ofvarious liquid substances that harden on the screw or applying anadditional layer of solid wear-resistant material to the portions of theextruder screw subject to wear. However, it has been found thatmaterials that project out from the surface of the screw are subject toshear during use, and the materials can experience fatigue cracks.Subsequently, pieces of the material can break off and end up beingincorporated in the extrudate being mixed. Often this necessitates thedisposal of batches of extrudate which are contaminated with pieces ofwear-resistant material or coating.

Another solution has been to cut grooves in the crests of the extruderscrew threads, and insert other materials, such as molybdenum, in thosegrooves, as shown in U.S. Pat. No. 5,135,378 to Catton (“Catton”). TheCatton process is, however, very complex, involving cutting a groove,laying in a first material along the sides and at intervals as bridgesacross the width of the groove, then laying in a second material in aliquid state that hardens to form a mechanical bond with the extruderscrew. The added material is then ground to form a smooth surface.

Another solution, as disclosed in U.S. Pat. No. 6,346,293 to Douris etal. (“Douris”), is to weld a bead of a hardened material along part ofthe width of the crest of the extruder screw threads, and then weldbeads of a different hardened material along either side of the firstbead of hardened material. Subsequently, the hardened materials areground to the required tolerances. Because of the many steps involved inwelding two separate materials to the crest of the screw, because of theneed for the materials that will bond to each other as well as to thescrew thread, and because of the grinding the hardened material, theprocess is very involved and time consuming. Thus, the Douris process israther expensive.

Therefore, a method and/or apparatus for extending the life of extruderscrews is needed by making them more resistant to wear wherein themethod does not compromise the structural integrity of the screw, norproduce fragments that contaminates the extrudate, and is not overlycomplex, involved or expensive.

SUMMARY

The present invention, accordingly, provides a method of applying aplurality of tiles to a flighting crest of at least one thread of anextruder screw. A groove is formed along the crest. Each tile is theninserted into the groove, wherein the tiles are in a spaced-apartarrangement. The tiles are then secured into the groove. In onepreferred embodiment of the present invention, the groove is formed inthe extruder screw when the extruder screw threads is cast. In yetanother preferred embodiment of the present invention, the groove is cutinto the crest after the extruder screw has been cast. In yet anotheralternative embodiment of the present invention, the tiles are furtherground to remove any protruding edges and to fit within the tolerancesof an extruder barrel. Another alternative embodiment of the presentinvention, further comprises inserting a spacer into spaces between thetiles; and securing the spacers.

In another preferred embodiment of the present invention, plates of awear-resistant material are secured to at least one leading edge of theextruder screw threads in a spaced-apart arrangement.

In one embodiment of the present invention, the tiles are made ofcarbide or tungsten-carbide. In another preferred embodiment of thepresent invention, the step of securing further comprises brazing,soldering, or gluing.

Additionally, the present invention also provides an apparatus forextruding. An extruding screw having at least one thread with a crestand having a groove formed therein is provided. Also, there are aplurality of tiles formed of a hardened materials secured within thegroove in a spaced-apart arrangement. In an alternative embodiment ofthe present invention, the hardened material is carbide ortungsten-carbide. In another alternative embodiment of the presentinvention the tiles are secured by brazing, soldering, or gluing. Inanother preferred embodiment of the present invention, spacers securedbetween the tiles.

Additionally, in yet another preferred embodiment of the presentinvention, a plurality of plates made of the hardened material aresecured to the crest in a spaced-apart arrangement.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiment disclosed may be readily utilized as a basisfor modifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an extruder screw embodying the featuresof the present invention;

FIG. 2 is a side view of an extruder screw embodying the features of thepresent invention; and

FIG. 3 is an enlarged cross-sectional view of a portion of an extruderscrew taken along line 3-3 of FIG. 2.

DETAILED DESCRIPTION

In the discussion of the FIGURES the same reference numerals will beused throughout to refer to the same or similar components. In theinterest of conciseness, various other components known to the art, suchas extrusion devices and extruder die plates have not been shown ordiscussed.

In the following discussion, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, itwill be obvious to those skilled in the art that the present inventionmay be practiced without such specific details. In other instances,well-known elements have been illustrated in schematic or block diagramform in order not to obscure the present invention in unnecessarydetail. Additionally, for the most part, details not considerednecessary to obtain a complete understanding of the present inventionhave been omitted, in as much as such details are considered to bewithin the skills of persons of ordinary skill in the relevant art.

Referring to FIGS. 1-3 of the drawings, the reference numeral 100generally designates an extruder screw of the present invention. Thesystem 100 includes a cast screw 10 and tiles 20. The tiles 20 aretypically made of carbide, tungsten-carbide, or some other hard,long-wearing material, and the cast screw is made of a cast metal orallow, such as steel.

As can be seen in FIG. 1, the wear-resistant layer is comprised of aseries of tiles 20 spaced slightly apart from each adjoining tile 20,rather than from a single piece of material. The purpose of spaced-aparttiles 20 is to provide sufficient flexibility so that the tiles 20 canmove slightly in relation to each other and the screw 10, and thereforewithstand shear and fatigue cracking that can occur when the extruderscrew is moving extrudate through the extruder. Thus, this spacing andthe resulting ability of the tiles 20 to move slightly prevents damageto the tiles 20 that results in pieces of the tiles 20 being broken offand falling into the extrudate.

In one arrangement of the present invention, generally flat tiles 20 areaffixed to the length of the flighting crest 12 of the threads 14 of theextruder screw 10. The tiles 20 are generally brazed, soldered, or gluedto the flighting crest 12 of the extruder screw threads 14.

In another arrangement of the present invention, the tiles 20 have agenerally flat upper surface, and a tapered base (not shown). Thetapered base portion (not shown) of the tiles 20 fit into a groove (notshown) that has been cut or cast into the flighting crest 12 in thescrew threads 14. The tiles 20 are generally brazed, soldered, or gluedinto the groove 16 in the flighting crest 12.

In another embodiment of the present invention, as seen in FIG. 1, thinplates of a hardened material 40 are affixed to the leading edge 18 ofthe screw 10. The plates 40 are brazed, soldered, or glued to theleading edge 18 of the screw 10. The plates 40 are spaced slightly apartfrom one another, rather than a single piece of material being affixedto the leading edge 18 of the screw 10. The purpose of spaced-apartplates 40 is to provide sufficient flexibility so that the plates 40 canmove slightly in relation to each other, and therefore withstand shearand fatigue cracking that can occur when the extruder screw is movingextrudate through the extruder. This spacing, and the resulting abilityof the plates 40 to move slightly prevents damage to the plates 40 thatresults in pieces of the plates 40 being broken off and falling into theextrudate. In some arrangements of the present invention, spacers 42 areinserted into the spaces between the plates 40. These spacers 42 aretypically made of a soft material, such as copper, that will move inresponse to movement of the plates 40 and/or the screw 10, andpreferably have a different expansion and contraction rate than thescrew 10 or the plates 40 for increased flexibility. If necessary, theplates 40 can be ground to achieve a smooth surface of the desireddimensions.

As can be seen in FIG. 2, some arrangements of the present inventionalso employ spacers 30 in conjunction with the tiles 20 used along theflighting crest 12. Spacers 30 are inserted into the spaces between thetiles 20. These spacers 30 are typically made of a soft material, suchas copper, that will move in response to movement of the tiles 20 and/orthe screw 10, and preferably have a different expansion and contractionrate than the screw 10 or the tiles 20 for increased flexibility.

After the tiles 20, and if used, spacers 30, have been affixed to theextruder screw flighting crest 12, they can be ground and polished tofit the tolerances of the extruder.

FIG. 3 shows a cross-section of an extruder screw 100 of the presentinvention after tiles 20 have been secured to the extruder screwflighting crest 12 and been ground to tolerance.

It is understood that the present invention can take many forms andembodiments. Accordingly, several variations may be made in theforegoing without departing from the spirit or the scope of theinvention.

Having thus described the present invention by reference to certain ofits preferred embodiments, it is noted that the embodiments disclosedare illustrative rather than limiting in nature and that a wide range ofvariations, modifications, changes, and substitutions are contemplatedin the foregoing disclosure and, in some instances, some features of thepresent invention may be employed without a corresponding use of theother features. Many such variations and modifications may be consideredobvious and desirable by those skilled in the art based upon a review ofthe foregoing description of preferred embodiments. Accordingly, it isappropriate that the appended claims be construed broadly and in amanner consistent with the scope of the invention.

1. A method of applying a plurality of tiles to a flighting crest of atleast one thread of an extruder screw, the method comprising: forming agroove along the crest; inserting each tile of the plurality of tilesinto the groove, wherein the tiles are in a spaced-apart arrangement;and securing the tiles into the groove.
 2. The method of claim 1 whereinthe groove is formed in the crest of the extruder screw threads when theextruder screw is cast.
 3. The method of claim 1 wherein the groove iscut into the crest after the extruder screw has been cast.
 4. The methodof claim 1 wherein the step of securing further comprises brazing,soldering, or gluing.
 5. The method of claim 1 wherein the tiles aremade of carbide or tungsten-carbide.
 6. The method of claim 1 furthercomprising inserting a spacer into spaces between the tiles in thegroove and securing the spacers.
 7. The method of claim 1 furthercomprising grinding the tiles to remove any protruding edges and to fitwithin the tolerances of an extruder barrel.
 8. The method of claim 1further comprising securing plates of a wear-resistant material to atleast one leading edge of the extruder screw threads in a spaced-apartarrangement.
 9. The method of claim 8 wherein the step of securing theplates further comprises brazing, soldering, or gluing.
 10. The methodof claim 8 wherein the wear-resistant material is carbide ortungsten-carbide.
 11. A method of applying a plurality of tiles ofwear-resistant material to a flighting crest of at least one thread ofan extruder screw, the method comprising: positioning the tiles on theflighting crest in a spaced-apart arrangement; and securing the tiles tothe crest.
 12. The method of claim 11 further comprising grinding thetiles to remove any protruding edges and to fit within the tolerances ofan extruder barrel.
 13. The method of claim 11 wherein the step ofsecuring further comprises brazing, soldering, or gluing.
 14. The methodof claim 11 wherein the wear-resistant material is carbide ortungsten-carbide.
 15. The method of claim 11 further comprising securingplates of a wear-resistant material to at least one leading edge of theextruder screw in a spaced-apart arrangement.
 16. The method of claim 15wherein the step of securing plates further comprises brazing,soldering, or gluing.
 17. The method of claim 15 wherein thewear-resistant material is carbide or tungsten-carbide.
 18. The methodof claim 11 further comprising inserting a spacer into the spacesbetween the tiles; and securing the spacers to the crest.
 19. Anapparatus for extruding, comprising: an extruding screw having at leastone thread with a crest having groove formed therein; and a plurality oftiles formed of a hardened materials secured within the groove in aspaced-apart arrangement.
 20. The apparatus of claim 19, wherein thehardened material is carbide or tungsten-carbide.
 21. The apparatus ofclaim 19, wherein the tiles are secured by brazing, soldering, orgluing.
 22. The apparatus of claim 19, wherein the apparatus furthercomprises spacers secured between the tiles.
 23. The apparatus of claim19, wherein the apparatus further comprises a plurality of plates madeof the hardened material secured to a leading edge of the apparatus in aspaced-apart arrangement.
 24. The apparatus of claim 23, wherein thehardened material is carbide or tungsten-carbide.
 25. The apparatus ofclaim 23, wherein the plates are secured by brazing, soldering, orgluing.
 26. The apparatus of claim 23, wherein the apparatus furthercomprises spacers secured between the plates.